Electroplating process



, develop a chemical graining method.

United States Patent-O 2,911,295 ELECTROPLATING PROCESS Carl F. Cooper,Grass Lake, Mich. N Drawing. Filed Jan. 14, 1958, Ser. No. 708,767

14 Claims. (Cl. 204-43) The present invention relates to anelectroplating bath of particular value for the deposition of zinc onaluminum and is a continuation-in-part of my prior filed applicationSerial No. 402,149, filed January 4, 1954, and now abandoned.

The electroplating of zinc on steel has become a widely practicedart.However the electroplating of zinc on aluminum to form zinc plates ofsubstantial thickness is practically unknown in the electroplating arts.In those fields where zinc plating has been used a wide variety ofaddition agents have been suggested for the refining of the grainstructure of the zinc, the obtaining of leveling action, the improvementin adhesion, and the like. Among these suggestions which is ofparticular interest here is a unique, suggestion by Weanin Patent No.2,646,397, issued July 21, 1953. In the Wean patent. it is disclosedthat a small proportion of titanium, that is about .005 ounce-.02 ounceof titanium per gallon of electrolyte, has the effect of leveling thesurface of a zinc plate on steel.

- As stated above the use of zinc plating on aluminum has been verylimited and is limited generally to the thin plates produced by thezincating method as a preplate for copper, nickel, and chrome. Industryhas practically no use for a zinc plate on aluminum where the zinc plateis to remain exposed. An outstanding exception to this statement howeverlies in the lithographic art. In lithography it is now quite common touse aluminum sheets which have one, two, or three layers of variousmetals placed thereon. In this art, however, it has been found necessaryto grain the aluminum by the use of arather involved and costly.metho-d, involving. rolling marbles and a sandy slurry over the surfaceof the aluminum for periods in excess of one hour in order to provide atype of grain on the aluminum which can serve for the later lithographicfunctions. In this connection the printed art notes frequently the hopethat someday someone will In passing and because it may seem pertinent Imay mention that I have tried the Wean bath mentioned above in thisconnection as well as all other baths of the art and have secured noresults favorable to the lithographing art.

It is therefore an object of this invention to treat the surface ofaluminum in a manner such as to produce an electroplate thereon having agrained metal surface suitable for use in the lithographic arts.

It is a further object of this invention to electroplate zinc onaluminum in a manner such as to have control of the grain size,porosity, and the like of the deposited metal in a manner as to efiectadvantages in lithography.

It is still a further object to electroplate zinc on aluminum to form avery adherent plate suitable as a preplate for the plating of a widevariety of other metals on aluminum as a basis metal;

I have now found that the foregoing and related objects can be securedin an electroplating bath comprising essentially at least about grams ofdissolved zinc per liter and dissolved titanium, wherein saidcompositions 2,977,295 Patented Mar. 28, 1 951 "ice are furthercharacterized by the concentration of dissolved titanium beingsuflicient and the acidity of the solution being suflicient such thatthe solution manifests at plating temperatures a yellow to yellow browncolor as opposed to the emerald green color of solutions more acidic andthe brown color of solutions less acidic and as opposed to the clear,grey-pink, and grey-blue colors of solutions less concentrated intitanium.

Although the concentration of dissolved zinc should be-in excess ofabout 10 grams perliter of solution I prefer a concentration of about 35grams per liter. I also prefer that the zinc be added aszinc fiuoborateeither in the form of the salt or by prior dissolving of the zinc metalin fiuoborate acid. Portions of the zinc fiuoborate may be replaced byzinc chloride but it ispreferred 'that the fiuoborate be used in excessover the chloride.

Larger amounts of zinc can be used but in general no additionaladvantage is obtained in concentrationsgreater than about grams ofdissolved zinc per liter.

The concentration of dissolved titanium can be stated generally to be inexcess of about 10 grams of dissolved titanium per liter. However theminimum effective concentration of titanium can be better expressed interms of the color properties of the solution. In this latter connectionthe acidity of the solution can also be most accurately defined inconnection with color. I have found that in very minor concentrations oftitanium such as that in the Wean patent mentioned above the color ofthe solution varies from clear to grey-pink to grey-blue depending onthe acidity of the solution. However, as the concentration of titaniumis increased and as the acidity of the solution is increased over thoseacidities normally associated with acid zinc electroplating baths thereoccurs a very definite series of color changes which can be used tocharacterize the solution quite accurately. Actually the acidity ofthese solutions is so great that it is difiicult to determine themaccurately on ordinary laboratory instruments. However, as oneapproaches these low pH ranges he notes the solution has first a browncolor which, upon becoming more acidic, gradually becomes a yellow toyellow brown color and, upon going to a still lower pH, takes on abright emerald green color. I have found that when the solution issufficiently concentrated in titanium ions and the acidity issufiiciently low to have attained the yellow brown color that I succeedin securing zinc plates on aluminum which have the necessary propertiesfor their use in the lithographic arts. On the contrary if the solutionis sufiiciently acidic to be emerald green or the solution issufiiciently less acidic to be in the brown color range the plating isnot successful. By successful plating in this case is meant platingwhere the grain of the zinc can be controlled in such a manner as toproduce very satisfactory lithographic plates. These plates are, inaddition, extremely adhesive and present a very beautiful blue whitecolor in contrast to the usual grey-white zinc plate.

It is preferred that the titanium be added as titanium fiuoborate andfurther it -is recommended that the bath be originally prepared bydissolving titanium in fiuoboric acid. This latter step is the mosteconomical since titanium can be secured as chips which are readilysoluble in fluoboric acid. There is no upper limit on the concentrationof titanium and it can be used to saturation. I have frequently platedwith titanium fiuoborate precipitate in the bath with complete success,

In addition to its use in the lithographic arts the zinc plate isextremely valuable when applied generally to steel, aluminum alloys, andmagnesium alloys. Its corrosion resistance is particularly noteworthy.In cornparative tests against standard galvanizing and zincelectroplating methods on steel my bath was able to produce coatingsmore adhesive and corrosive resistant than the standards.

In connection with my invention there has been considerable controversyamong experts as to the part played by titanium in the actual plateitself. For the reason of this controversy I do not wish my invention tobe limited by theory or in any way defined by a presumed action oftitanium in the plated metal itself. In this connection for example,independent laboratory tests have shown, in one instance, that titaniummetal had actually diffused or plated into the aluminum basis metal toform the alloy AL3TI. In other cases of spectroscopic analysis titaniumwas reported in the zinc plate and with the opinion that there was somesort of solid solution formed. Other experts, when titanium was found inthe zinc plate, merely express the opinion that the titanium wascaptured as an impurity from the bath. Whatever may be the facts aboutthe part titanium plays because its actual physical presence in theplate itself, there is no question but what it does alter the overallplating operation. Plating may be conducted in the bath of the inventionby' the use of zinc anodes, inert anodes, or by the combination of zincand titanium anodes. I have found it preferable to use mostly zincanodes with some titanium anodes, the latter being just sufiicient tomaintain the concentration of titanium in the plating solution.

The temperatures of the baths for plating purposes can be generally from80 F. to 150 F., the bath giving -well defined continuous plates at allthese temperatures.

A wide variety of current densities can be used, although 24-36 amperesper square foot at 2-3 volts is satisfactory.

. Example I A plating bath was made up as follows: 1050 grams oftitanium and 850 grams of zinc were dissolved in fiuoboric acid (47%)and sufficient water added to make 6.5 gallons. The concentration of theforegoing solution is approximately about 35 grams of zinc and 40 gramsoftitanium per liter. The pH of the solution was adjusted until itreached a yellow brown color at the plating temperature of 110 F. Aseries of steel and aluminum alloys were plated in the bath at a currentdensity of 36 amperes per square foot and 3 volts. All plated sampleswere very adherent, were of a white blue color and yielded a verycrystalline appearing surface. The plates were subjected to standardadhesion and salt spray tests and were found equal to or better sheetsin the above composition which sheets were sub mitted for tests in thelithographing field and declared excellent by independent experts. Inthe latter connection the crystalline surface of the zinc acted much inthe manner of the previously grained plates. A wide variety of aluminumalloys have been plated in the above bath including 248T, 52S, 25, 13Hand the like.

Example II The previous example was repeated in hundreds of individualbaths except that zinc in varying amounts from zero grams per literupward to saturation, titanium ion concentrations from zero up tosaturation, and pH ranges from less than zero on standard laboratorymeters to approaching alkaline solutions were evaluated. In addition awide variety of standard organic addition agents such as corn syrup,sugar, gelatin, licorice and the like were used. It was in this fashionthat the limits stated within this specification were obtained. A widevariety of steel alloys, aluminum alloys, copper and magnesium alloyswere plated. a

Example III Grams Titanium fiuoborate 220 Zinc fiuoborate 45 Zincchloride Water to 1 liter.

The above solution can be adjusted with fiuoboric acid or sodiumhydroxide as the case may be to secure a yellow brown color. Plating wascarried out on a variety of aluminum alloys to produce a beautifulcrystalline zinc plate. The plate was extremely adhesive. The solutionwas then adjusted gradually with amounts of corn syrup up to 10 cc. perliter and amounts of gelatin up to 2 grams per liter to produce platesof various degrees of leveling. The final solution yielded a perfectlysmooth, uniform plate with no apparent crystalline'extensions beyond theplane of the plate.

I claim:

1. An aqueous composition suitable for the electroplating of zinc on ametal selected from the group consisting of aluminum, steel andmagnesium, said composition comprising essentially in solution at leastabout 10 grams of zinc per liter and at least about 10 grams of titaniumper liter, the principal negative ions of said solution being fiuoborateions; said solution being maintained sufficiently acidic so that itmanifests a yellow to yellow brown color as opposed to the emerald greencolor of solutions more acidic and the brown color of solutions lessacidic.

2. The composition of claim 1 wherein said solution is maintainedsufiiciently acidic by adjustment of its fiuoborate ion content.

3. An aqueous composition suitable for the electroplating of zinc on ametal selected from the group consisting of aluminum, steel andmagnesium, said composition comprising essentially in solution at leastabout 10 grams of zinc per liter and at least about lO grams of titaniumper liter, fiuoborate ions as the principal negative ions, and chlorideions in a concentration less than that of the fiuoborate ions; saidsolution being maintained sufiiciently acidic so that it manifests ayellow to yellow brown color as opposed to the emerald green color ofsolutions more acidic and the brown color of solutions less acidic.

4. An aqueous composition suitable for the electroplating of zinc on ametal selected from the group con: sisting of aluminum, steel andmagnesium, said composition comprising essentially in solution titaniumfiuoborate providing at least about 10 grams of titanium per liter andat least about 10 grams of zinc per liter derived from a member of thegroup consisting of zinc chloride and zinc fiuoborate; said solutionbeing maintained sufficiently acidic so that it manifests a yellow toyellow brown color as opposed to the emerald green color of solutionsmore acidic and the brown color of solutions less acidic.

5. An aqueous composition suitable for the electroplating of zinc on ametal selected from the group consisting of aluminum, steel andmagnesium, said composition comprising essentially in solution about 35grams of zinc per liter and about 40 grams of titanium per liter, theprincipal negative, ionsof said solution being fluoborate ions; saidsolution being maintained sufiiciently acidic so that it manifests ayellow to yellow brown color as opposed to the emerald green color ofsolutions more acidic and the brown color of solutions less acidic.

6, An aqueous composition suitable for the electroplating of zinc on ametal selected from the group consisting ofaluminum, steel andmagnesium, said composition consisting essentially in solution of atleast about 10 grams of zinc per liter and at least about 10 grams oftitanium per liter; saidv solution being maintained sufficiently acidicso that it manifests a yellow to yellow brown color as opposed to theemerald green color of solutions more acidic and the brown color ofsolutions less acidic.

7. An aqueous composition suitable for the electroplating of zinc on ametal selected from the group consisting of aluminum, steel andmagnesium, said composition consisting essentially in solution of atleast about grams of zinc per liter and at least about 10 grams oftitanium per liter, the principal negative ions of said solution beingfluoborate ions; said solution being maintained sufficiently acidic sothat it manifests a yellow to yellow brown color as opposed to theemerald green color of solutions more acidic and the brown color ofsolutions less acidic.

8. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 1, the basis metal being the cathodetherein.

9. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 2, the basis metal being the cathodetherein.

10. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 3, the basis metal being the cathodetherein.

11. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 4, the basis metal being the cathodetherein.

12. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 5, the basis metal being the cathodetherein.

13. The method of electroplating zinc on a basis metal selecting fromthe group consisting of aluminium, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 6, the basis metal being the cathodetherein.

14. The method of electroplating zinc on a basis metal selected from thegroup consisting of aluminum, steel and magnesium; said methodcomprising passing an electrical current through an electroplating bathcomprising the composition of claim 7, the basis metal being the cathodetherein.

References Cited in the file of this patent UNITED STATES PATENTS2,646,397 Wean July 21, 1953

1. AN AQUEOUS COMPOSITION SUITABLE FOR THE ELECTROPLATING OF ZINC ON AMETAL SELECTED FROM THE GROUP CONSISTING OF ALUMINUM, STEEL ANDMAGNESIUM, SAID COMPOSITION COMPRISING ESSENTIALLY IN SOLUTION AT LEASTABOUT 10 GRAMS OF ZINC PER LITER AND AT LEAST ABOUT 10 GRAMS OF TITANIUMPER LITER, THE PRINCIPAL NEGATIVE IONS OF SAID SOLUTION BEING FLUOBORATEIONS; SAID SOLUTION BEING MAINTAINED SUFFICIENTLY ACIDIC SO THAT ITMANIFESTS A YELLOW TO YELLOW BROWN COLOR AS OPPOSED TO THE EMERALD GREENCOLOR OF SOLUTIONS MORE ACIDIC AND THE BROWN COLOR OF SOLUTIONS LESSACIDIC.